The present invention relates to an automatic strand take-up installation. Even more precisely it relates to a strand take-up installation intended to be used in a below-bushing chopping process, in which process thermoplastic strands, especially glass strands, are both drawn and chopped. According to another aspect of the invention, it also relates to a process for direct chopping with a bushing equipped with this automatic strand take-up installation.
It will be recalled that the manufacture of glass reinforcement strands results from a complex industrial process that consists in obtaining strands from molten glass streams that flow out through the orifices in bushings. These streams are drawn, from at least one fiberizing cabin, into the form of continuous filaments, these filaments are then gathered into base strands, and then these strands are for example chopped continuously so as to produce a plurality of glass strands. This phase of the industrial process is commonly called “direct below-bushing chopping”.
Conventionally, a fiberizing cabin essentially consists of a molten glass feed coming from a furnace, this glass at high temperature feeding a plurality of bushings made of a platinum alloy, which glass, after passing through orifices made in the bushing and being drawn, creates filaments.
In a direct below-bushing chopping process, the filaments, after having received a sizing composition and having been combined into strands, are directed to a chopper which carries out both the drawing operation and the operation of chopping the strands into chopped glass strands.
Conventionally in a below-bushing chopping process, this operation is carried out by a bushing machinist and takes place, during a normal production cycle, many times, as it is part of the technology and the operation of a below-bushing chopper.
The latter must draw the glass strands at a constant speed corresponding precisely to the steady-state output of the bushing. Now, to achieve this steady state, it is necessary to pass via a transient phase that consists essentially in progressively increasing the strand drawing speed. This transient phase is also present after any unexpected interruption to the production, such as for example when the strands break. It is necessary to pass via a transient restart phase that requires the strand to be drawn at a moderate speed, which can be obtained by hand or by an individual strand-puller placed beneath the sizing device for each bushing.
In principle, when the bushing machinist judges that the bushing is thermally stabilized, he takes hold of the strand coming from the strand-puller for this bushing and directs it onto a restart member located after the chopping members, the restart member being designed to switch the strand drawing speed from a speed of the order of a few m/s (from 1 to 5 m/s) to a few tens of m/s, which in fact corresponds to the nominal drawing speed reached in the steady state.
When this nominal speed is reached, the strands are directed onto the actual chopping member, generally consisting of an anvil wheel and a blade wheel, these being designed to output its chopped glass strands after the strands have passed between them.
Now, it will be understood that this back-and-forth movement between the bushing and the restart wheel of the chopper may take place according to programmed phases and according to non-programmed phases of the production cycle.
With regard to programmed phases, there are those that correspond to maintenance work, which requires the operation of the machine to be interrupted and the chopping member changed for example.
As regards non-programmed phases, these may especially involve work by the machinist when a breakage occurs in at least one of the strands at any point between the bushing exit and the actual chopper.
Whatever the nature of the phases, the machinist will have to move many times back and forth, which may take a not inconsiderable amount of time (especially when there are faults with several bushings). This results in a loss of final product (chopped glass strands) and the production of waste, and finally results in a reduction in efficiency of the production unit.
A direct below-bushing chopper installation for partly solving this problem is known, especially from U.S. Pat. No. 5,935,289. This installation is equipped with a mechanized device in the form of a shuttle that makes it possible, on the one hand, to take up at least one strand bundle and, on the other hand, to deposit the latter at the below-bushing chopper.
The major drawback of the above installation lies in its large size. This is because the mechanized device for taking up and depositing the strand bundle moves along a frame that faces the production installation, extending from vertically beneath the bushings as far as the actual chopper. This “curtain” arrangement constitutes a risk as regards work carried out by the bushing machinist, the safety of the latter possibly being jeopardized by the unexpected passage of the shuttle.
The present invention therefore aims to alleviate these drawbacks by proposing a sate installation that makes it possible to limit the operator's back-and-forth movements between the plurality of juxtaposed fiberizing cabins and the chopper.